A Purdue University study found that certain fats in salad dressings could boost your body’s absorption of the salad’s nutrients — which means some of those low-fat dressings might prevent your body from absorbing the maximum amount of vitamins and minerals in your salad. Now, before you go out and buy the biggest bottle of ranch you can find, let us clarify: When we say fats, we mean the healthy kind.

Researchers gave 29 participants salads with three different types of salad dressings — butter (saturated fat), canola oil (monounsaturated fat), and corn oil (polyunsaturated fat) — and tested how much of the salads’ carotenoids were absorbed into the body when served with dressings containing 3 grams, 8 grams, or 20 grams of fat. They found that monounsaturated fat-rich dressings required the least amount of fat to get the most carotenoid absorption, while saturated fat and polyunsaturated fat dressings required higher amounts of fat to get the same benefit, according to ScienceDaily.

The more polyunsaturated fats in a dressing, the more carotenoids were absorbed. The amount of nutrients absorbed into the bloodstream didn’t change with fat dosage in the monounsaturated-fat dressings; just as many nutrients were absorbed with a 3-gram serving of monounsaturated fats as a 20-gram serving. And saturated fats were slightly dose-dependent, but didn’t show as much of a difference in absorption with dosage as researchers noticed in polyunsaturated fats.

Hopefully your salad dressing doesn’t contain high amounts of saturated fat anyway, even if it does increase your body’s absorption of nutrients; they’re not as bad as trans fats, but you should definitely keep them to a minimum in your diet. Diets high in saturated fat have been linked to coronary heart disease. The Dietary Guidelines for Americans recommends Americans consume less than 10 percent of daily calories as saturated fats.

Monounsaturated and polyunsaturated fats, on the other hand, can have positive health effects when eaten in moderation. As long as you’re not consuming too much, they can help reduce bad cholesterol and lower your risk of heart disease and stroke. Plus, polyunsaturated fats offer omega-6 and omega-3, essential fats that your body needs but can’t produce itself.

"If you want to utilize more from your fruits and vegetables, you have to pair them correctly with fat-based dressings," said Mario Ferruzzi, the study’s lead author and a Purdue associate professor of food science. "If you have a salad with a fat-free dressing, there is a reduction in calories, but you lose some of the benefits of the vegetables."

The study, which was published online in the journal Molecular Nutrition & Food Research and funded by the U.S. Department of Agriculture, suggests that if you’re looking for a low-fat salad dressing option, you should choose one with monounsaturated fats since you’re going to get just as many nutrients from the low-fat version as you would from the high-fat version. But if you’d prefer a healthy salad dressing that helps you get the most nutrients out of your salad, you might opt for a salad dressing higher in polyunsaturated fats.

"Overall, pairing with fat matters," Feruzzi said. "You can absorb significant amounts of carotenoids with saturated or polyunsaturated fats at low levels, but you would see more carotenoid absorption as you increase the amounts of those fats on a salad."

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